Airborne beacon antenna



14. 1956 R. KRAUSZ ET AL AIRBORNE BEACON ANTENNA 4 Sheets-Sheet 1 FiledJan. 2, 1952 FlG.l

INVENTORS ROBERT KRAUSZ DONALD L. MARGERUM ATTORNEY Feb. 14. 1956 R.KRAUSZ ET AL 2,735,093

AIRBORNE BEACON ANTENNA Filed Jan. 2, 1952 4 Sheets-Sheet 2 FIG. 5

\ IN V EN TORS ROBERT KRAUSZ BY DONALD L. MARGERUM ATTORNEY Feb. 14,1956 KR ET AL 2,735,093

AIRBORNE BEACON ANTENNA v FIG. 7

INVENTORJ ROBERT KRAUSZ DONALD L. MARGERUM Maw 44% ATTORNEY Feb. 14.1956 Filed Jan. 2, 1952 R. KRAUSZ ET AL 2,735,093

AIRBORNE BEACON ANTENNA 4 Sheets-Sheet 4 FIG. 8

INVENTORS ROBERT KRAUSZ BY DONALD L. MARGERUM ATTORNEY ORNE BEACONANTENNA Robert Krausz, Los Angeles, and Donald L. Margerum,

Long Beach, Calif., assignors to North American Aviation, Inc.

Application January 2, 1952, Serial No. 264,481

9 Claims. (Cl. 343725) This invention relates to beacon antennae forpropagation of microwave electromagnetic energy, and particularly to abeacon antenna adapted to propagate circularly polarized electromagneticwaves.

Airborne beacon antennae must be designed to operate in conjunction withground radar. Since ground radar devices may employ either circularlypolarized radiation or plane polarized radiation with orientation uponwhich it is desired not to place any limitation, the beacon must respondto and must propagate circularly polarized electromagnetic waves. Sincean aircraft carrying a beacon must be capable of detection from anydirection in the horizontal plane, the pattern of propagation must besuch as to cause substantially uniform propagation from any direction ofobservation of the aircraft, and the pattern of propagated circularlypolarized waves must be as large as possible.

This invention contemplates an antenna for propagating electromagneticwaves with a substantially toroidal pattern.

It is an object of this invention to provide a beacon antenna adapted topropagate circularly polarized electromagnetic waves over a considerableportion of its propagation pattern.

Other objects of invention will become apparent from the followingdescription taken in connection with the accompanying drawings, in whichFig. l is an elevational view of the invention partly in section;

Fig. 2 is a side view of the invention;

Fig. 3 is a sectional view of the device shown in Fig. 1 taken at 33 inFig. 2;

Fig. 4 is an elevational view partly in section of a second embodimentof the invention;

Fig. 5 is a side view of the device shown in Fig. 4;

Fig. 6 is a sectional view taken at 6-6 in Fig. 4;

And Figs. 7 and 8 are plots of the radiation pattern achieved by theinvention.

Referring now to the drawings, and particularly to Fig. 1, there isshown a coaxial wave guide consisting of a cylindrical conductor 1surrounded by a hollow dielectric cylinder 2 which in turn is encased ina tubular conductor 3. Tubular conductor 3 is connected to a fitting 4which is adapted to be connected to a coaxial wave guide not shown.Tubular conductor 3 has cut in its periphery a pair of longitudinaldiametrally opposed slots 6 having a length equal to approx mately halfthe wave length of the electromagnetic waves to be propagated by thedevice. Attached to tubular conductor 3 and extending through dielectriccylinder 2 are a number of conducting pins 5 which extend radiallytoward conductor 1. Cylindrical skirt 8, having slots 9 of substantiallythe same dimensions as slots 6, is provided to prevent the flow oflongitudinal currents upon the outer surface of tubular conductor 3below the upper end of the skirt. Conductor 1 extends beyond the end ofconductor 3 to form a dipole with conductor 3.

In operation, a coaxial wave guide is connected to fitting 4 to supplyelectromagnetic energy transmitted through the guide in the TEM mode.This energy is conducted nited States Patent 0 2,735,093 Patented Feb.14, 1956 upon the inside surface of tubular conductor 3 and upon theoutside surface of conductor 1 in the same mode. When the energy reachespins 5, nonsymmetrical modes of the electromagnetic energy aregenerated, and approximately one-half of the energy is radiated fromslots 6. The energy radiated from slots 6, of course, is polarized in ahorizontal direction since electric fields exist across the slots. Theremainder of the electromagnetic energy proceeds to the ends of the twoconductors and is radiated with vertical polarization from the dipoleelements 1 and 3. The distance between the end of conductor 1 and theend of tubular conductor 3 is made one-quarter of the wave length of theelectromagnetic energy being transmitted. Likewise, the distance betweenthe upper end of skirt 8 and the end of tubular conductor 3 isapproximately onequarter wave length. Slots 6 are located as near aspracticable to the dipole in the interest of compactness. Consequently,the energy radiated by the slots is in phasequadrature with the energyradiated by the dipole. This arrangement results in circularly polarizedwaves radiated in that portion of a plane perpendicular to the axis ofthe two conductors which is opposite the two slots. The circularpolarization of the electromagnetic Waves adjacent one slot is opposedin sense to the polarization adjacent the other slot. Since pins 5present a discontinuity to electromagnetic waves transmitted withintubular conductor 3 it is necessary to adjust the penetration of pins 5and their position along conductor 3 in order to prevent an impedancemismatch which would result in the reflection of energy back through thecoaxial wave guide. Actually, each such pin causes a reflection, but byproper spacing of the pins in relation to the wave length of the energybeing transmitted, the reflections may be caused to substantially cancelout at or near the operating frequency.

In order to simplify the problem of impedance matching in the deviceshown in Figs. 1 and 2, the embodiment of the invention shown in Figs.4, 5, and 6 has been devised. In Fig. 4, the invention has been modifiedby substitution of a sector of a hollow dielectric cylinder for hollowdielectric cylinder 2 shown in Fig. 1. Sector '7, as shown in Fig. 6,extends from a point near slots 6 to a point on the opposite side oftubular conductor 3 such that the axis of symmetry of the sector isnormal to a plane bisecting the slots longitudinally. The electric fieldis then distorted, as shown in Fig. 6, and radiation from slots 6results as shown. Pins 5, of course, are no longer necessary, since nocoupling means other than the sector is required to radiate energy fromthe slots. To assure a proper impedance match between the wave guide andthe antenna it is necessary only to vary the length of dielectric sector7. With this arrangement it has proved possible to achieve a frequencybandwidth of 1 /g% at an operating frequency of 3000 megacycles, thefrequency bandwidth Referring to Fig. 7, there is shown a plot of theradiation pattern of the invention in a plane normal to the axis of thewave guide with the abscissa aligned with the plane of the slots. Theradiation pattern of the slots is shown as a solid line, whereas theradiation pattern of the dipole is shown as a dotted line. Thus,circular polarization occurs opposite the slots and over a considerableangle on either side thereof.

The radiation pattern of the device in a plane including the axis of thewave guide and the slots is shown in Fig. 8. Here, the substantiallytoroidal shape of the radiation pattern is demonstrated. Thus it isevident that the device is capable of propagating electromagnetic wavesin a substantially toroidal pattern with circular polarization thereofover a considerable portion of the pattern. If it is desired to restrictthe area in which circular polarization occurs to the region oppositeonly one of the slots, it is necessary only to eliminateone of the slotsand make a slight adjustment of the exciting means. The radiationpatternfrom the single slot is then that of Fig. 7-with butone lobe from theslot.

Although the invention has been described and illustrated in detail,-itis to-be clearly understood that thesame is by way of illustration andexample only and is not to be taken by way of limitation, the spirit'and scope of this invention being limited only by the-terms of theappended claims.

We claim:

1. Means for radiating circularly polarizedelectroma netic wavescomprising a coaxial waveguide, a tubular conductor connected to saidwave guide at one end and having near its free end an axial slot oflength equal to one-half the wave length of saidelectromagnetic waves acylindrical conductor centered within said tubular conductor andprotruding from the free end thereof, a-spacer of dielectric materialbetween said conductors, and means for coupling half the electromagneticenergy in said waveguide out said slot the remainder being propagatedfrom the end of said cylindrical conductor withpolarization in phase-,quadrature with the electromagnetic waves propagated from said slotwhereby circularly polarized energy is radiated.

2. A beacon antenna for propagating electromagnetic waves in asubstantially toroidal pattern said waves being circularly polarizedover a considerable portion of said pattern comprising a coaxial waveguide for transmitting electromagnetic waves in the TEM mode, a dipoleat the end of said wave guide oriented to propagateelectrornagneticwaves with a plane polarization parallel to the axis of said guide, anaxial slot cut in the outside of said coaxial wave guide and situatednear said dipole, andmeans for exciting said slot to thereby propagatefrom said slot electromagnetic waves plane polarized normal to the axisof said guide and in phase-quadrature with waves propagated from saiddipole whereby circularly polarized waves are propagated from saidantenna over an area opposite said slot.

3. A device as recited in claim 2 and further comprising a second slotcut in said coaxial wave guide and diametrally opposed to said firstslot to thereby propagate circularly polarized waves opposite both saidslots.

4. A device as recited in claim 2 in which said exciting means comprisesa plurality of discontinuitiesiin the interior of said guide adjacentsaid slot to thereby distort the electric and magnetic fields to causepropagation of electromagnetic waves from said slot.

5. A device as recited in claim 2 in which said exciting means comprisestwo complementary sectors of a cylinder filling said coaxial wave guide,said sections being of material having differing dielectric constantsarranged symmetrically with respect to the electromagnetic wavestransmitted in said guide are distorted to cause propagation from saidslot.

6. An antenna for propagating electromagnetic waves in a substantiallytoroidal pattern, said waves being circularly polarized over aconsiderable portion of said pattern, comprising a coaxial wave guideincluding two coaxial conductors separated by a dielectric hollowcylinder, a dipole at the end of said wave guide oriented to propagateelectromagnetic waves with a plane polarization parallel to the axis ofsaid guide and in a substantially toroidal pattern, a longitudinal slotin the outer conductor of said coaxial wave guide situated near saiddipole, and a pinrality of pins adjacent said slot and extending fromsaid outer conductor radially towardsaid inner conductor'for excitingsaid slot to propagate electromagnetic waves in phase-quadrature withthe electromagnetic waves propagated by said dipole whereby planepolarized electromagnetic waves are propagated in a toroidal patterncentered on the axis of said guide and circularly polarizedelectromagnetic waves are propagated in a region opposite said slot.

7. An antenna for propagating electromagnetic waves in a substantiallytoroidal pattern, said waves being circularly polarized in a substantialportion of said pattern, comprising a coaxial wave guideincluding twocoaxial conductors, a dipole at the end of said wave guide oriented topropagate electromagnetic waves with plane polarization parallel to theaxis of said guide, and in a substantially toroidal pattern, a pair ofdiametrallyopposed longitudinal slots in the outer of said twoconductors situated near said dipole, and a non-uniform dielectricmedium separating said conductorsinthe region .of;said;slots for causingsaid slots to propagate electromagnetic waves in phasequadraturewith-:the electromagnetic waves, propagated-by said dipole whereby planepolarizedgelectromagnetic waves are propagated in atoroidalpatterncentered on the .axis of said guide and circularly polarizedelectromagnetic waves arepropagated in regions opposite said: slots.

:8. An antenna for propagating electromagnetic waves in asubstantiallytoroidal pattern with circular polarization throughout. a substantialportion of: said pattern, com- .prising acoaxial waveguide includingtwo'coaxialconductors, .a dipole ,at thelendof said waveguideoriented topropagate electromagnetic waves'with plane polarization parallel to theaxis of said guide, a pair of diametrally opposed longitudinalslots inthe outer of ,said two conductors situated near said ,dipole andapluralityof radially disposed pins extending inwardly-from said outerconductorlin the vicinity of said slots ;tocause;said-slots to propagateelectromagnetic waves in phase-quadrature withvthe electromagnetic wavespropagated fromsaid dipole without an impedance mismatch with said,guide whereby plane polarized waves are propagated in a toroidalpatterncentered on the 'axisof said guide and circularly polarizedelectromagnetic waves are propagated-opposite said slots.

9. An antenna for propagating electromagnetic waves .in a substantiallytoroidal pattern with circular polarization throughout a portion of saidpattern comprising acoaxial wave guide including two coaxialconductors,a dipole at the end of said waveguide .oriented-togpropagateelectromagnetic waves with plane polarization parallel to the axis ofsaid guide, a longitudinal slot in theouter of said two conductorssituated near said dipole and a nonuniformdielectric medium-separatingsaid conductors tocause said slot to propagate electromagnetic waves in-phasequadrature with -the electromagnetic waves propagated from saiddipole without an impedance mismatch with said guide whereby planepolarized waves zaregpropagated ina toroidal pattern centered on theaxis of ,said guide and circularly polarized electromagnetic waves arepropagatedopposite said slot.

References Cited in the file of this patent V UNITED STATES PATENTS

